The present application relates to Double-Base Bidirectional Bipolar transistors, and more particularly to power transistors of the general type known as “B-TRANs.”
Note that the points discussed below may reflect the hindsight gained from the disclosed inventions, and are not necessarily admitted to be prior art.
Published U.S. application US 2014-0375287 disclosed a fully bidirectional bipolar transistor, having emitter/collector regions on both faces of a semiconductor die, and also having base contact regions on both faces. In one group of embodiments (shown e.g. in FIG. 13A of that application, and described in paragraph [0083]), the emitter/collector regions are laterally separated from the base contact regions by a dielectric-filled trench. This reduces same-side carrier recombination in the ON state.
Application US 2014-0375287 also describes some surprising aspects of operation of the device. Notably: 1) when the device is turned on, it is preferably first operated merely as a diode, and base drive is then applied to reduce the on-state voltage drop. 2) Base drive is preferably applied to the base nearest whichever emitter/collector region will be acting as the collector (as determined by the external voltage seen at the device terminals). 3) A two-stage turnoff sequence is preferably used. 4) In the off state, base-emitter voltage (on each side) is limited by a low-voltage diode which parallels that base-emitter junction.
A somewhat similar structure was shown and described in application WO2014/122472 of Wood. However, that application is primarily directed to different structures. The Wood application also does not describe the methods of operation described in the US 2014-0375287 application. The Wood application also does not appear to describe lateral trench isolation between emitter/collector regions and base contact regions.
The present application provides improvements in structures of this type, in methods of operating such structures, and in systems which incorporate such structures.
The present application teaches, among other innovations, a symmetrically bidirectional dual-contact base bipolar junction transistor, in which both of the emitter/collector regions, which are present on both (opposed) surfaces of a semiconductor die, are surrounded by a field plate in a trench. This field plate separates the emitter/collector regions from adjacent base contact regions. Since base contact regions are present on both surfaces of the device, this structure improves the breakdown voltage of whichever base contact region is on the collector side, without degrading the characteristics of the base contact region on the other side. This provides surprising improvement in the breakdown voltage of a device like that of US 2014-0375287.
The present application also teaches, among other innovations, methods of operating structures of this type, and systems which incorporate structures of this type.